Informing interventions to improve uptake of adjuvant endocrine therapy in women with breast cancer: a theoretical-based examination of modifiable influences on non-adherence

PURPOSE: To inform intervention development, we measured the modifiable determinants of endocrine therapy (ET) non-adherence in women with breast cancer, using the Theoretical Domains Framework (TDF) and examined inter-relationships between these determinants and non-adherence using the Perceptions and Practicalities Approach (PAPA). METHODS: Women with stages I–III breast cancer prescribed ET were identified from the National Cancer Registry Ireland (N = 2423) and invited to complete a questionnaire. A theoretically based model of non-adherence was developed using PAPA to examine inter-relationships between the 14 TDF domains of behaviour change and self-reported non-adherence. Structural equation modelling (SEM) was used to test the model. RESULTS: A total of 1606 women participated (response rate = 66%) of whom 395 (25%) were non-adherent. The final SEM with three mediating latent variables (LVs) (PAPA Perceptions: TDF domains, Beliefs about Capabilities, Beliefs about Consequences; PAPA Practicalities: TDF domain, Memory, Attention, Decision Processes and Environment) and four independent LVs (PAPA Perceptions: Illness intrusiveness; PAPA Practicalities: TDF domains, Knowledge, Behaviour Regulation; PAPA External Factors: TDF domain, Social Identity) explained 59% of the variance in non-adherence and had an acceptable fit (χ(2)(334) = 1002, p < 0.001; RMSEA = 0.03; CFI = 0.96 and SRMR = 0.07) Knowledge had a significant mediating effect on non-adherence through Beliefs about Consequences and Beliefs about Capabilities. Illness intrusiveness had a significant mediating effect on non-adherence through Beliefs about Consequences. Beliefs about Consequences had a significant mediating effect on non-adherence through Memory, Attention, Decision Processesg and Environment. CONCLUSIONS: By underpinning future interventions, this model has the potential to improve ET adherence and, hence, reduce recurrence and improve survival in breast cancer. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00520-023-07658-x.